Regeneration of spent supported metal catalysts

ABSTRACT

A method for regenerating spent supported metal catalysts comprising treating the spent catalyst with an organo-metallic complex forming agent having an ionization constant pK 1  of at least 2.5. The catalyst activity is restored to an activity level near to or greater than the fresh catalyst. The regeneration method is particularly useful for regenerating spent palladium catalysts on an alumina support as utilized for the hydrogenation of ethyl anthraquinone (EAQ) in the production of hydrogen peroxide.

RELATIONSHIP TO PENDING APPLICATIONS

[0001] This application is a continuation-in-part of pending U.S. patentapplication Ser. No. 09/745,510, filed Dec. 22, 2000.

FIELD OF THE INVENTION

[0002] The invention relates to the regeneration of spent supportedmetal catalysts including metals comprising noble metals and metalsgenerally described as non-noble metals. The support material for themetal catalyst may comprise any solid material useful as a catalystsupport. The invention particularly relates to a process forregenerating spent supported noble metal catalysts; but especiallypalladium catalysts utilized for the hydrogenation of ethylanthraquinone (EAQ) for producing hydrogen peroxide (H2O2) product. Theregenerated catalyst activity levels of the catalyst of the inventionare near or greater than those of the fresh catalyst.

BACKGROUND OF INVENTION

[0003] The conventional production of hydrogen peroxide product involvesa two-step process in which a hydrogen donor solvent, ethylanthraquinone (EAQ), is first hydrogenated and then oxidized with oxygento form the hydrogen peroxide product. In some hydrogen peroxidemanufacturing facilities, the hydrogenation step is carried out in afixed bed reactor utilizing a palladium-on-alumina or similar catalyst.A typical catalyst may contain 0.28 to 0.33 wt % palladium on a largepore alumina support. The useful life expectancy of the catalyst isabout two years, after which its activity drops to about 30% of itsoriginal (fresh catalyst activity) condition or level. It is believedthat this catalyst deactivation is caused by deposition of highmolecular weight organic materials formed from the polymerization of EAQon the active sites of the catalyst, and/or by gradual agglomeration ofthe palladium to larger particles or clusters on the catalyst. Spentpalladium/alumina catalysts are presently being regenerated using asimple “wash-burn” procedure, in which the catalyst is first extractedwith an organic solvent to remove any soluble material deposits; then,the spent catalyst is subjected to a controlled carbon burn-out step atabout 850° F. temperature in air. The high temperature regenerationtreatment may also promote undesirable agglomeration of the palladium tolarger particles on the catalyst support. Thus, it is difficult tosuccessfully regenerate the used catalyst back to near 100% of itsoriginal activity. In fact, the simple wash-burn procedure can usuallyrestore the used catalyst to only about 70% of its original or freshactivity level. Such “wash-burn” catalyst regeneration procedures havebeen disclosed by various U.S. and foreign patents. For example, U.S.Pat. No. 4,148,750 to Pine discloses a process for redispersal of noblemetals on used supported zeolite-containing catalysts. U.S. Pat. Nos.4,454,240 and 4,595,666 to Ganguli disclose method steps forregenerating used catalysts by dilute acid treatment to remove undesiredmetal deposits followed by carbon burn-off at increased temperaturelevels. Also, U.S. Pat. No. 5,188,996 to Huang et al disclosesredispersion of noble metal such as platinum on low acidity support suchas silica by contacting with chlorine and oxygen at low pressures.

[0004] An overall objective of the present invention is to overcome thelimitations inherent in prior art spent catalyst regeneration processesand provide a process that will restore spent catalyst activity to alevel at or near that of fresh metal-on-solid support catalyst. Afurther objective of the invention is to provide a regeneration processwith the foregoing capabilities that will be applicable generically tospent solid supported metal catalysts, regardless of composition. Aparticular objective is to improve the economics of the hydrogenperoxide production process by increasing the activity and service lifeof the palladium/alumina catalyst, as well as that of other similarsupported noble metal catalysts.

[0005] Based on an understanding at the molecular level of the apparentcatalyst reaction and deactivation mechanism, the surface structure ofthe catalyst support material, and the exposition of palladium crystalclusters thereon, an effective procedure has been developed forregenerating and enhancing used palladium/alumina catalyst to anactivity level significantly higher (90% or more) than that achieved bythe current “wash-burn” procedure. The procedure is applicable tocatalysts comprising both noble and non-noble metal-on solid supportwherein the solid support comprises any solid material useful as asupport for solid metal catalysts.

SUMMARY OF INVENTION

[0006] A method or process has been discovered for regenerating spentcatalyst comprising metal-on-solid support which returns the spentcatalyst to an activity level close to or even greater than the activitylevel of the fresh catalyst. The method is applicable to any metalcatalyst employed in combination with any metal catalyst supportfamiliar to those skilled in the art. Through an appreciation of themechanisms of the catalyst deactivation events occurring at themolecular level on the catalytic surface of a metal-on-solid supportcatalyst, it has been discovered that when spent catalyst particles aretreated with an organo-metallic complex forming agent the catalyticactivity of the spent catalyst can be restored in whole or substantiallyin part. Suitable organo-metallic complexing agents polymeric chemicalsand preferably small, polyfunctional organic molecules containing atleast one carboxylic acid group and exhibiting a pK₁ of at least 2.5.Typically, the preferred agents contain other functional groupsincluding hydroxyl and amino groups.

[0007] Although treatment of the spent catalyst particles withorgano-metallic complex forming agents is essential in the instantprocess to achieve strong catalyst reactivation, the treatment may alsoinclude other steps such as solvent washing of the spent catalyst ordrying and calcining of the spent catalyst, typically applied beforetreatment with organo-metallic complex forming agents.

[0008] For the fresh catalyst, the support material may comprise anycatalyst support material known in the art. Preferably noble metal areused for hydrogen peroxide production.The noble metals include palladium(Pd), platinum (Pt), gold (Au), iridium (Ir), osmium (Os), rhodium (Rh),rhenium (Re), or ruthenium (Ru), or combinations thereof, with palladiumusually being preferred. The invention is particularly useful forregenerating and enhancing used supported palladium (Pd) catalyst, suchas that utilized for hydrogenation of ethyl-anthraquinone (EAQ) forproducing hydrogen peroxide (H₂O₂) product.

[0009] In the manufacture of hydrogen peroxide using EAQ, the catalystis a noble metal on alumina support. The alumina has a surface area of20-600 m2/gm and pore diameters within the range of 50-600 Angstroms,with 50-500 m2/gm and 100-400 Angstroms being preferred.

[0010] The used catalyst regeneration method of this invention includesthe following basic step:

[0011] contacting the spent catalyst with a suitable organic treatingagent selected for forming an organo-metallic complex for breaking downlarge noble metal agglomerates on the used catalyst to smaller metalparticles, and redistributing the smaller noble metal(s) particles onthe catalyst support. Suitable catalyst treating agents should have anionization constant pK₁ greater than about 2.5.

[0012] A preferred method also includes the following additional stepscarried out before the treatment of the spent catalyst with theorgano-metallic complexing agent:

[0013] cleaning the used supported noble metal catalyst by solventextraction for removal of process contaminants and adsorbed chemicalsfrom the used catalyst by contact with suitable organic solvent(s);

[0014] drying and calcining the cleaned used catalyst to remove anypolymer deposits remaining on the catalyst.

[0015] The organic solvents suitable for the used catalyst cleaningmethod can be alcohols such as methanol, amines, ketones, or similarorganic compounds utilized at cleaning conditions of 0-200° C.temperature and 1 to 50 atm. pressure for 2-8 hours. Preferred solventcleaning conditions are 10-100° C. temperature and 1-20 atm. pressurefor 4-6 hours. Suitable catalyst drying and calcining conditions for themethod step (2) are heating the catalyst in air at 100-120° C. for 1-8hours for the drying, then further heating it in air at 200-600° C.(392-1112° F.) temperature for 1-24 hours for the calcining step.Calcining the dried catalyst at lower temperatures and longer timeperiods within these ranges is usually preferred for economic reasons.

[0016] The organo-metallic complex forming agents suitable in theinstant invention may be taken from small, polyfunctional, non-polymericchelate-forming chemicals or from oligomeric or polymeric polyfunctionalchelate-forming chemicals. The organo-metallic complex forming chemicaltreating agents suitable for the noble metal redistribution method arechemical compounds wherein, the treating agent exhibits an ionizationconstant pK₁ of at least about 2.5,

[0017] Examples of organo-metallic complex forming chemical treatingagents, some of which are useful in the present invention ,and theircorresponding ionization constants pK₁ are as follows: Treating AgentpK1 Oxalic Acid 1.27 EDTA 2.01 Citric Acid 3.13 Glycolic Acid 3.63Succinic Acid 4.21 Glycine 9.78 Salicylic Acid 13.12

[0018] Oxalic acid having a pK₁ of 1.27 and ethylene diaminotetraaceticacid (EDTA) having a pK₁ of 2.01 are outside the desired range, and arethereby not suitable for providing desired organo-metallic complexes forthis invention. Also, EDTA has been shown to remove aluminum fromzeolites by a chelation effect which can thereby render zeolite supportsineffective by deactivating the support. Useful reaction conditions forforming the organo-metallic complexes and for redistributing the noblemetal particles are 10-500° C. temperature and 1-10 atm. pressure for1-8 hours, with 20-450° C. temperature and 1-5 atm. pressure for 2-6hours being preferred. For best results, the organic treating agentshould preferably be maintained in its liquid phase; however aliquid/vapor phase mixture having only a small portion of vapor may beutilized.

[0019] By utilizing the catalyst regeneration method and procedureaccording to this invention, it is proved experimentally that usedpalladium (Pd) catalyst supported on alumina can be better cleaned forremoval of the process contaminants and polymer deposits, and thusexpose more catalyst surface and active Pd sites to a process reactant.Catalyst activity tests have also shown that used supported Pd catalystsregenerated by the method of this invention have their activitysignificantly increased to at least about 80% and preferably up to93%-103% of fresh catalyst activity level, compared to only about 70% offresh catalyst activity after being regenerated by known traditional“wash-burn” regeneration procedures. This regeneration method isparticularly useful for used supported catalysts containing 0.2-0.4 wt.% palladium deposited on a support of alumina or silica, as utilized forproducing hydrogen peroxide (H2O2) by hydrogenation ofethyl-anthraquinone (EAQ).

[0020] Advantages provided by the catalyst regeneration method andprocedure of this invention include its ability to not only effectivelyremove contaminants and organic deposits from the used noble metalcatalyst, but also to break apart and redistribute the active noblemetal molecules such as palladium in the pores of the catalyst support.This new catalyst regeneration method and procedure not only cleans thecontaminated catalyst surface, but also improves the exposition anddistribution of the noble metal(s) such as palladium on the catalystsupport. The regeneration procedure can restore catalyst activity to100% or more of the fresh catalyst standard, and the resulting molarselectivity ratio of desired product to side products is 190:1, which isa better molar selectivity ratio than that achieved for fresh catalyst(150:1). This catalyst regeneration procedure and method is considereduseful for regenerating supported noble metal catalysts containing othernoble metals instead or in addition to palladium. After such usedcatalyst regeneration, the process reactants have improved contact withthe catalyst active metal(s) particles and thereby enhance the activityand product selectivity of the catalyst.

BRIEF DESCRIPTION OF DRAWINGS

[0021] FIGS. 1(a)-1(d) show schematic illustrations of typicaldeposition of noble metal(s) such as palladium in the pores of thesupport for fresh, spent and regenerated supported palladium catalysts,respectively.

DETAILED DESCRIPTION OF INVENTION

[0022] In general, the invention relates to the reactivation orregeneration of spent supported metal catalysts. The method is based onthe use of a metal complexing agent, which is an organic compound havingthe ability to form organo-metallic complexes with the catalytic metalcomponents of a supported catalyst. By forming these complexes, themetal complexing agent causes the catalytic metal components of asupported spent catalyst to be rearranged on the surface of the catalystsupport.

[0023] The utility of the rearrangement process derives from the typicalphysical structure of spent (deactivated) catalysts. Frequently, theactive metal components of supported catalysts have undergoneagglomeration or sintering during use, such that metal particles thatwere originally small in size for the fresh catalyst become much largerfor the deactivated catalyst. This leads to a drop in active surfacearea and a corresponding loss in activity.

[0024] In the present invention, the regeneration method allows most orall of the lost activity to be recovered. In the process of formingorgano-metallic complexes, the large metal particles on the supportsurface are broken up. The metals are redeposited or rearranged assmaller particles, with some even smaller than in the original freshcatalyst. This allows the activity of the catalyst to be recovered atleast to activity levels that are a large percentage of the originalcatalytic activity, and in some cases to levels that can even equal orexceed the catalytic activity of the fresh catalyst.

[0025] In the parent patent application to which this invention isrelated, the use of the method of the invention was disclosed toregenerate supported noble metal catalysts, where the noble metal isplatinum, palladium, gold, osmium, iridium, rhodium, ruthenium, andcombinations thereof and where the support for the catalyst is alumina.As disclosed herein, It has been discovered that the regeneration methodis useful for other catalysts and support material, as follows:

[0026] A. Applicable Catalysts and Support Material

[0027] 1. The regeneration method is useful for supported catalystswhere the solid support comprises any solid material useful as acatalyst support. This support may be porous or non-porous. It may beused in the form of so-called structured materials, such as structuredpacking, which may be in the form of controlled shapes such as rings,saddles, or other shapes, or may be in the form of larger structures,examples of which include structured packings commonly used fordistillation and other phase contacting equipment which involve the useof regular geometric arrangements of convoluted surfaces. Supports mayalso be in the form of firms, membranes, coatings, or other mainlytwo-dimensional structures. Supports may also be in the form of mainlyspherical particles (i.e. beads).

[0028] The catalyst support may comprise oxide materials, including butnot limited to alumina, silica, titania, kieselguhr, diatomaceous earth,bentonite, clay, zirconia, magnesia, as well as the oxides of variousother metals, alone or in combination. They also include the class ofporous solids collectively known as zeolites, which have ordered porousstructures. The catalyst support may comprise carbon-based materials,including but not limited to carbon black, activated carbon, graphite,fluoridated carbon, and the like, or combinations thereof. The catalystsupport may comprise organic solids, such polymers, including thepolymer membranes which are used in the electrodes of fuel cells., andpolymeric or resinous particles such as are used as ion exchange resinsor adsorbents. The catalyst support may comprise a metal or metal alloy.

[0029] 2. The regeneration method is useful for regeneration of spentsupported metal catalysts where the supported catalytic particlescomprise a noble metal, where the noble can be platinum, palladium,rhenium, gold, osmium, iridium, rhodium, ruthenium, and combinationsthereof.

[0030] 3. The regeneration method is useful for regeneration of spentsupported catalysts where the supported catalytic particles comprise, inwhole or in part, catalytic components other than noble metals. Thesecan include catalytic metals including but not limited to nickel,copper, iron, cobalt, zinc, silver, chromium, vanadium, titanium,molybdenum, tungsten, manganese, scandium, or combinations thereof. Theycan include other (non-transition) metals including but not limited toaluminum, gallium, indium, tin, antimony, lead, bismuth, or combinationsthereof. They can include alkali or alkali earth metals including butnot limited to sodium, potassium, lithium, beryllium, calcium,magnesium, or combinations thereof. They can include rare-earth metals(lanthanides or actinides) including but not limited to lanthanum,cerium, or combinations thereof. They can include non-metals orsemi-metals including but not limited to boron, carbon, nitrogen,oxygen, fluorine, phosphorus, silicon, sulfur, chlorine, germanium,arsenic, selenium, bromine, tellurium, iodine, or combinations thereof.

[0031] B. The Regeneration Method with Complexing Agents

[0032] The required method for catalyst regeneration of the subjectinvention is contacting a spent or used catalyst with a complex formingagent. The complex forming agent is a chemical compound defined by itsability to form complexes with the supported catalytic components of thespent catalyst. In the case of catalysts where the supported catalyticmaterial is composed predominantly of a metal or metals, the preferredcomplexing agent is a chelating agent capable of forming a strongorgano-metallic complex called a chelate.

[0033] The complexing agent breaks up catalytic particles on the surfaceof the support, and redistributes or rearranges the catalytic componentsto form a new supported catalyst structure that is characterized bysmaller catalytic particles. These smaller particles may also be of moreuniform size, and/or more uniformly distributed that those on the spentcatalyst, although this is not essential.

[0034] Useful complexing agents include but are not limited to:

[0035] a. Mono, di and tribasic aliphatic and aromatic carboxylic acids,hydroxy carboxylic acids, amino carboxylic acids and organo sulfonicacids including glycolic acid, malonic acid, tartaric acid, citric acid,succinic acid, glutaric acid, glycine, salicylic acid, isophthalic acid,2-aminobenzoic acid and the like, and their salts.

[0036] b. Polymers and copolymers, including polyacrylates andmethacrylates, polyvinybenzoates, polyvinylsulfate, polyvinylsulfonates, polybiphenol carbonates, polybenzimidazoles,polyvinylpyrrolidone, polypyridines, and the like.

[0037] c. Aliphatic and aromatic amino compounds, including ethylenediamine, propylene diamine, diethylenetriamine, triethylenetetraamine,diethylenetriamine pentaacetic acid (DTPA),N-(hydroxyethyl)-ethylenediaminotriacetic acid (HEDTA), and the like,and their salts.

[0038] d. Phosphonate compounds, such as those marketed under theDequest brand by Solutia, including amino tri(methylanephosphonic acid)(ATMP), 1-Hydroxy-1,1diphosphonic acid (HEDP), diethylenetriamine penta(methylphosphonic) acid, and the like, and their salts.

[0039] The process conditions for forming the organo-metallic complexesof spent supported catalytic metals include a temperature of 0° C. to500° C., and a mole ratio of spent catalytic metal particles tocomplexing agent of 1:100 to 100:1. The preferred operating conditionsinclude a temperature of 50-500° C. at atmospheric pressure. The spentcatalytic metal particles are treated with the organic complexing agentwith the complexing agent preferably dissolved in water or othersolvents such as methanol, glycolic acid and acetic acid, or any solventthat can dissolve the organo-metallic complexing agent. The treatmenttime is preferably about 5 hours, or between one and 10 hours. Followingtreatment, the regenerated catalyst is separated from residualcomplexing agent by conventional means. The regenerated catalyst may berecovered and used directly in the catalytic process without furthertreatment. Depending upon the chemistry of the process in which theregenerated supported metal catalyst is being used, e.g., EAQhydrogenation, the regenerated catalyst can be used in that processwithout resorting to the separation of the regenerated catalyst from theorganic complexing agent mixture.

[0040] Optionally, the spent catalyst may also be subjected to otherprocessing steps, either before or after the complexing agent treatmentstep. These other steps can include but are not limited to washing witha liquid solvent, filtration, drying, calcination, or reduction, orcombinations thereof.

[0041] The method for the regeneration of spent supported metal catalystparticles of the invention comprises contacting the spent particles witha suitable organic treating agent to form an organo-metallic complex onthe catalyst under conditions sufficient to break down large catalystparticle clusters whereby the resulting smaller particles areredistributed in the pores of the support material by contact with theorgano-metallic complex forming agent. The organometallic complexingagent preferably has an ionization constant pK₁ of greater than 2.5.Suitable treating agent contacting conditions are 10-500° C. temperatureat 1-10 atm. pressure for 2-8 hours.

[0042] The catalyst overall regeneration method and procedure developedfor the used supported noble metal catalysts, such as palladium (Pd)catalyst on alumina support, may include the following specific steps:

[0043] cleaning the used supported Pd catalyst having organic depositsby contact with a selected liquid cleaning solvent such as methanol at0-200° C. temperature and 1-50 atm. pressure to dissolve andsubstantially remove the organic deposits from the catalyst;

[0044] drying the used catalyst at 100-120° C. temperature for 1-8 hoursto remove the cleaning solvent from the catalyst;

[0045] calcining the cleaned catalyst in air at 200-600° C. temperaturefor 1-24 hours to remove any remaining organic deposits from thecatalyst;

[0046] adsorbing a suitable organic treating agent selected for formingan organo-metallic complex on the catalyst, and breaking down large Pdparticle clusters and relocating or redistributing the resulting smallerpalladium particles in pores of the support material by contact with theorgano-metallic complex forming agent liquid and vapor, such as glycolicacid having ionization constant pK₁ of 3.63.

[0047] When utilizing the supported palladium on alumina catalyst forproducing hydrogen peroxide product from ethyl anthraquinone (EAQ), thecritical diameter of intermediate EAQ:H2 dimer molecules is about 120 Å.Therefore, the ideal pore diameter of the alumina support should be atleast about 1.5 and preferably about 2.0 times that of the dimermolecules, i.e. at least about 180 Å and preferably at least 240 Å, soas to allow free movement of the reactant dimer from the adsorbed siteon the catalyst. During the used catalyst regeneration, it is desirableto break up Pd particle clusters from pores having diameter smaller thanabout 180 Å, and relocate the resulting smaller palladium particles intopores having diameters larger than about 180 Å. It is also desirable toavoid depositing the Pd particles into the catalyst pores having a sizesmaller than about 180 Å. Thus, for this used palladium catalystregeneration method, it is desirable to relocate the Pd particles fromthe pores smaller than about 180 Å into those pores larger than 180 Å,and preferably larger than 240 Å.

[0048] The four main reasons for the used supported Pd catalystdeactivation during hydrogenation of ethyl anthraquinone (EAQ) toproduce hydrogen peroxide are: (1) contamination of the Pd catalyst bypoisoning chemicals in the process feed or solvent; (2) coke depositionor large polymer molecule formation blocking the active Pd sites; (3) Pdparticles agglomeration to form clusters; and (4) Pd leaching from thecatalyst. The first three reasons for catalyst deactivation are at leastpartially reversible by regeneration, but the Pd loss by leaching isirreversible. After the palladium is lost from the catalyst, it is notpossible to restore the catalytic activity to near its initial ororiginal level, unless the palladium particle size after regeneration issmaller than that of fresh catalyst.

[0049] Experimental data have indicated some catalyst deactivation dueto the first three listed reasons. Theoretical understandings of thereaction mechanism, catalyst structure and deactivation provide thebasis for designing this improved catalyst regeneration method andprocedure for used or spent supported noble metal catalysts, such assupported palladium catalysts. In order to regenerate the spent catalystto a highly active and product selective state, the regeneration methodpreferably should achieve the following requirements:

[0050] solvent clean the used Pd catalyst surface to substantiallyremove its contaminants and organic deposits,

[0051] breakdown the large Pd particles cluster on the catalyst tosmaller particles,

[0052] and relocate the smaller Pd particles from small pores to thosehaving a diameter larger than about 180Å.

[0053] Experimental results have shown that the first two goals wereachieved, and it is believed that the third goal also was achieved, asthe regenerated catalyst activity and selectivity results indicate thatthe Pd was redistributed or relocated to a desirable state on thecatalyst support. Although theoretical consideration are not intended tolimit the scope of the invention, when a suitable organo-metalliccomplex forming and redistributing agent such as glycolic acid isutilized, the following effects on the Pd particles are believed tooccur: (1) The reaction between Pd clusters and glycolic acid treatingagent breaks down the large Pd clusters to the smaller clusters andparticles. (2) The glycolic acid agent helps to intercalate in betweenthe Pd particles, thus allowing a more even distribution of these metalparticles on the support. (3) The glycolic acid treating agent can alsoenter the pores smaller than 180 Å and react with Pd. When morePd-glycolate complexes are formed, the pores are too small to hold allthe complexes, and the Pd-glycolate material is sequentially squeezedout of pores smaller than 180 Å. After these Pd glycolates move into thelarger pores, several Pd-glycolates will combine together by hydrogenbonding to form a large Pd-glycolate cluster, and this effect willprevent the Pd from depositing into the pores smaller than 180 Å.

[0054] The surface of typical fresh and spent supported palladium (Pd)catalysts, and catalyst regenerated according to this invention, areshown schematically in FIGS. 1(a)-1(d). As seen in FIG. 1(a), thesurface of fresh catalyst is clean, and the Pd particles are depositedrandomly in both small and large pores due to the catalyst traditionalnon-particle-size control preparation procedure. For the used or spentsupported noble metal catalyst (FIG. 1b), due to the long termexposition of catalyst under the reaction conditions the Pd particleshave agglomerated to form larger clusters, thereby at least partiallyblocking the catalyst small pores. The organic deposits are also formedon the Pd surface and alumina support, and can block more small pores.These effects result in a significant decrease of catalyst activity,surface area, and percentage of pores smaller than about 200 Åexposition.

[0055] Traditional catalyst regeneration methods involve heating toabout 450° C. (842° F.) temperature for several hours can clean thecatalyst surface (FIG. 1c). However, the sintering of Pd during suchcatalyst heating forms larger particles which block the entrance of manysmall pores of the support. The low surface exposition of large Pdparticles results in limited access of reactants to the active Pd, thusleading to a less active catalyst than the fresh catalyst standard. FIG.1d depicts the condition of the catalyst surface after regenerationwherein pore blockage has been reduced or removed and the surfaceexposition has been restored to that approximating the surface of freshcatalyst.

[0056] This invention will be further described by reference to thefollowing example, which should not be construed as limiting the scopeof the invention.

EXAMPLE

[0057] Samples of used supported palladium (Pd) on alumina catalyst,obtained from extended operations for hydrogenation of ethylanthraquinone (EAQ) for producing hydrogen peroxide (H2O2) product, wereregenerated utilizing the method of this invention. The used catalystcontained 0.2-0.4 wt. % palladium on alumina support. The used catalystwas first contacted with methanol solvent at 25° C. and ambient pressurefor 3.3 hours, and then replaced with new methanol solvent three timeswith each time for 30 minutes (0.5 hour). Then the washed catalyst wasdried in air at 110° C. for 2 hours, and then calcined in air at 400° C.for 4 hours. The calcined catalyst was then treated with glycolic acidagent at 400° C. and ambient pressure for 3 hours. The results obtainedwith the used catalyst that was regenerated by this procedure are shownin Table 1, and are depicted schematically in FIG. 1(d). TABLE 1Regeneration of Used Supported Palladium Catalyst Fresh Used Wash-BurnRegenerated Catalyst Surface Area, m2/g 82.6 80 76.7 88.1 Pores Diameter< 240 Å, % 9.5 13.0 Desired Product/Side Product Molar Ratio 150:1 190.5Catalyst Activity Relative to Fresh Catalyst, % 100 ˜30 70 90-103

[0058] From the above results, it is noted that after the catalyst wascleaned by methanol solvent and re-generated by contact with glycolicacid treating agent, its surface area increased to 88.1 m2/g, which isdesirably greater than that of the fresh catalyst standard (82.6 m2/g).The percentage of pores <240 Å also increased to 13.0% from 9.5% for thespent catalyst. These results indicate that the catalyst regenerationmethod of this invention not only cleans all the organic deposits fromthe used catalyst, but also clears the blockage of small pores in thesupport, which means that the large Pd particles on the used catalystwere broken down to smaller particles for the regenerated catalyst.Also, the increased surface area indicates that the Pd particle size issmaller than that of the fresh standard, and the particles are depositedmainly in the larger pores, otherwise the catalyst surface area wouldnot increase significantly. This explanation is fully supported by thecatalyst activity and selectivity test results.

[0059] Used catalyst regenerated by the method of the present inventionhas an activity close to or even exceeding 100% of the fresh catalyststandard. Because the spent catalyst had been used for years, someattrition of Pd from the support is unavoidable, but this new catalystregeneration procedure restored the activity to near 100% or more of thefresh standard activity. This result indicates that for the regeneratedcatalyst the Pd active metal is being used more efficiently, e.g. the Pdis exposed on the catalyst surface in smaller particle size and atlocations which are easy for process reactants to reach, i.e. in poreslarger than about 240 Å diameter.

[0060] The molar ratio of desired _(hydrogenation) product to sideproduct after the catalyst regeneration (190:1) also exceeded that forthe fresh catalyst standard (150:1). The high selectivity is apparentlyan effect of Pd deposited in pores >240 Å. As discussed above, to avoidover hydrogenation of EAQ:H₂ dimer and formation of the undesiredproduct EAQ:H₄, one must try to minimize the time during which EAQ:H₂remains at the adsorbed site, and this intermediate material must beremoved as soon as possible. The critical diameter of intermediateEAQ:H₂ dimer is about 120 Å. Ideally, it should be avoided to deposit Pdinto the catalyst pores that have a diameter smaller than 240 Å, and inwhich the free movement of the dimer is restricted and excesshydrogenation is unavoidable.

[0061] Although the invention has been described broadly and also interms of specific preferred embodiments, it will be understood thatmodifications and variations may be made to the invention as definedwithin the scope of the following claims.

What is claimed is:
 1. A method for regenerating spent supported metalcatalyst particles comprising: contacting the spent catalyst with atleast one organo-metallic complexing agent having a pK₁ of at least 2.5under conditions sufficient to regenerate the spent supported metalcatalyst.
 2. The method of claim 1 wherein the supported metal catalystcomprises noble metal catalysts selected from the group consisting ofsupported palladium, platinum, rhenium, gold, osmium, iridium, rhodium,ruthenium, and combinations thereof.
 3. The method of claim 1 whereinthe supported metal catalyst includes metals selected from the groupconsisting of nickel, copper, iron, cobalt, zinc, silver, chromium,vanadium, titanium, molybdenum, tungsten, manganese, scandium, aluminum,gallium, indium, tin, antimony, lead, bismuth, sodium, potassium,lithium, beryllium, calcium, magnesium, lanthanum, cerium, andcombinations thereof.
 4. The method of claim 1 wherein said metalsfurther include non-metals and semi-metal selected from the groupconsisting of boron, carbon, nitrogen, oxygen, fluorine, phosphorus,silicon, sulfur, chlorine, germanium, arsenic, selenium, bromine,tellurium, iodine, and combinations thereof.
 5. The method of claim 1wherein said support comprises porous and nonporous supports selectedfrom the group consisting of alumina, silica, titania, kieselguhr,diatomaceous earth, bentonite, clay, zirconia, magnesia, zeolites,carbon black, activated carbon, graphite, fluoridated carbon, organicpolymers, metals, metal alloys, and combinations thereof.
 6. The methodof claim 1 wherein the organo-metallic complexing agent comprises anorganic chelating agent.
 7. The method of claim 6 wherein said chelatingagent comprises aliphatic or aromatic mono, di, and/or tribasiccarboxylic acids.
 8. The method of claim 7 wherein said aliphatic oraromatic mono, di, and/or tribasic carboxylic acids are selected fromthe group consisting of glycolic acid, malonic acid, tartaric acid,citric acid, succinic acid, glutaric acid, glycine, salicylic acid,isophthalic acid, 2-aminobenzoic acid, and their salts.
 9. The method ofclaim 6 wherein said chelating agent comprises polymers selected fromthe group consisting of polyacrylates and polymethacrylates,polyvinybenzoates, polyvinylsulfate, polyvinyl sulfonates, polybiphenolcarbonates, polybenizimidazoles, polyvinylpyrrolidone, andpolypyridines.
 10. The method of claim 6 wherein said chelating agentcomprises aliphatic and aromatic amino compounds including ethylenediamine, propylene diamine, diethylenetriamine, triethylenetetraamine,diethylenetriamine pentaacetic acid (DTPA),N-(hydroxyethyl)-ethylenediaminetriacetic acid (HEDTA), and the like,and their salts.
 11. The method of claim 6 wherein said chelating agentcomprises phosphonate compounds including amino tri(methylanephosphonicacid) (ATMP), 1-Hydroxy-1, 1diphosphonic acid (HEDP), diethylenetriaminepenta (methylphosphonic) acid, and their salts.
 12. The method of claim1 where said organo-metallic complexing agent comprises an oligomericand/or polymeric chelating agent containing one or more acid groups. 13.The method of claim 1 including the further steps of cleaning, dryingand calcining the spent catalyst before contacting the spent catalystwith said organo metallic complexing agent.
 14. The method of claim 1wherein said conditions comprise temperature of 0-400° C. at 0-10atmospheres of pressure.
 15. The method of claim 1 wherein saidconditions include a treatment time of 1-8 hours.
 16. A method forregenerating spent supported metal catalyst particles comprising: a)calcining the spent catalyst in air; and; b) contacting the calcinedcatalyst with at least one organo-metallic complexing agent, whereby thespent catalyst is regenerated to a catalyst activity level of 90-103% offresh catalyst activity.
 17. The method of claim 16 including thefurther step of cleaning the spent catalyst in contact with a solventbefore calcining.
 18. The method of claim 17 wherein the spent catalystis cleaned at 10-100° C. temperature and 1-20 atmospheres pressure for atime sufficient to clean the surface of the supported catalystparticles.
 19. The method of claim 16 wherein the spent catalyst iscalcined in air at 350-500° C. temperature for 2-10 hours.
 20. Themethod of claim 16 wherein the calcined catalyst is contacted with atleast one organo-metallic complexing agent at 20-400° C. temperature and1-5 atmospheres for a time sufficient to regenerate the catalyst. 21.The method of claim 16 wherein the organo-metallic complexing agent hasa pK₁ of at least 2.5.
 22. The method of claim 16 wherein the supportedmetal catalyst comprises noble metal catalysts selected from the groupconsisting of supported palladium, platinum, rhenium, gold, osmium,iridium, rhodium, ruthenium, and combinations thereof.
 23. The method ofclaim 16 wherein said organo-metallic complexing agent is selected fromthe group consisting of aliphatic and aromatic mono, di, and/or tribasiccarboxylic acids, polyacrylates and polymethacrylates,polyvinybenzoates, polyvinylsulfate, polyvinyl sulfonates, polybiphenolcarbonates, polybenizimidazoles, polyvinylpyrrolidone, polypyridines,ethylene diamine, propylene diamine, diethylenetriamine,triethylenetetraamine, diethylenetriamine pentaacetic acid (DTPA),N-(hydroxyethyl)-ethylenediaminetriacetic acid (HEDTA), aminotri(methylanephosphonic acid) (ATMP), 1-Hydroxy-1, 1diphosphonic acid(HEDP), diethylenetriamine penta (methylphosphonic) acid, their salts,and combinations thereof.
 24. The method of claim 16 wherein thecatalyst support is selected from the group consisting of alumina,silica, titania, kieselguhr, diatomaceous earth, bentonite, clay,zirconia, magnesia, zeolites, carbon black, activated carbon, graphite,fluoridated carbon, organic polymers, metals, metal alloys, andcombinations thereof.